In Italian applications No. 21922 A/78 and 28527 A/78 (corresponding to U.S. Pat. No. 4,268,666); of the same Assignee a process is described for obtaining solutions of cellulose derivatives, ordinarily called "methylol derivatives" even though their exact chemical structure is not certain, in organic solvents, particularly dimethylformamide (DMF), dimethylacetamide (DMAC) and N-methylpyrrolidone. Said process consists in contacting cellulose with paraformaldehyde and with the solvent at high temperature, preferably 120.degree. C.-130.degree. C. The molar ratio of CH.sub.2 O units of the formaldehyde to anhydroglucosidic units of the cellulose (hereinafter called, for the sake of brevity, "CH.sub.2 O/ cellulose ratio") is about 13 and is then reduced, by degassing or in other ways, even down to 3, to facilitate the coagulation of the cellulose derivative in suitable coagulating baths and the subsequent regeneration of the cellulose, which permit the production of formed bodies, e.g. filaments, of regenerated cellulose.
The cellulose content of the solutions is at most about 14-15% (all the percentages and parts in this description are by weight). It is obvious that it would be desirable to prepare solutions at higher cellulose concentration which would render the spinning more efficient and would permit the use of smaller amounts of solvents, which must then be recovered.